Besides the Oil Cooler Hoses just getting old and leaking some Members have had their Drivers side (US modesels) Motor Mounts collaspe and have the Power Steering Belt cut through one of the Oil Cooler Hoses.
I have only read of this happening ounce but someone had the Plastic Oil Supply line to the Fuel Injection Pump Crack and leak out Oil.
Is it Engine Oil or Transmission Fluid; the Transmission Cooler lines are the as are the Power Steering Lines.
If a Oil Cooler Hose or Hoses need replacing remember that there is a chance that the Aluminum Nipples on the Oil Cooler may strip the threads when the Oil Cooler Hose is removed.
If you have a 617.* there is a repair for that.
Oil Cooler Repair pics and parts.
Has part number for screwed nipple Search = Screwed nipple 915013-013002
Oil cooler repair - help needed...
I the DIY section there is also a way to avoid stripping the threads where you make 2 length wise cuts on opposite sides of the Oil Cooler Hose nuts. And, stick something in the cut and split the Nuts apart.
If you ding up the Oil Cooler Nipple Threads that is not a serious issue because the Hoses do not seal on the threaded area of the Nipples.
I do not know if the repair proceedure will apply for either of your vehicles; 1990 300SEL/1987 300TDT. But, the splitting of the Oil Cooler Line Nuts ought to work on all of them if there is room to get at them.